It is well known in the art to alkylate phenols having at least one unsubstituted ortho position. Many prior art processes have been disclosed as being non-selective and indiscriminate in regard to the nature of the products that are formed. Winkler et al., U.S. Pat. No. 2,448,942, for example, discloses a process for the preparation of penta-substituted phenols. The Winkler et al patent mentions that one may employ either alcohol or methyl ether in the vapor phase using various metal oxides such as aluminum oxide, barium oxide, manganese oxide, magnesium oxide, calcium oxide, etc. as the catalyst. Alumina is the preferred catalyst. The Winkler et al process, however, is somewhat indiscriminate and lacks specificity for ortho-alkylation to the relative exclusion of alkylation in the meta- and para- positions.
Winkler et al. teach that the reaction is carried out at superatmospheric pressures at temperatures in the range of 300.degree. C. to about 450.degree. C. However, temperatures of about 430.degree. C have been noted, e.g., in Hamilton, U.S. Pat. No. 3,446,856, to cause a decrease in the yield of alkylated product. When phenol and methanol are reacted at temperatures above 450.degree. C, Hamilton teaches that the production of hexamethyl benzene, a non-phenolic product, is favored. For reactions of methanol with phenol, xylenol or cresol, Hamilton stated that a temperature of about 350.degree. to 430.degree. C is favored in order to obtain high yields of alkylated product, while temperatures below 350.degree. C increase the yield of ether by-products. Temperatures of above 450.degree. C and superatmospheric pressures cause decomposition of the reactant and favor the production of unwanted materials. The Hamilton process was based on the discovery that magnesium oxide was a selective ortho-alkylation catalyst that was useful at atmospheric pressure at a defined temperature range.
U.S. Pat. Nos. 3,707,569 and 3,751,488 are based respectively, on the discoveries that certain tellurium-containing compounds and molybdic acid salts are useful as selective ortho-alkylation catalysts. Further, U.S. Pat. No. 3,764,630 describes a method for selectively alkylating a phenol compound with an alkanol in the presence of water and a catalytically active compound such as molybdenum oxide and alkali metal, alkaline earth metal, lead, bismuth and ammonium salts of molybdic acid in admixture with magnesium oxide. Also, U.S. Pat. No. 3,843,606 discloses a catalyst which is porous magnesium oxide powder bonded with an inert organic cellulosic polymeric binder for use in selective alkylation of phenols. Lastly, U.S. Pat. No. 3,873,628 discloses mixtures of magnesium oxide and manganese sulfate as useful catalysts for ortho-alkylation of phenols. These patents are incorporated herein by reference.
Ortho-alkylated phenols have valuable properties. They are particularly useful as the starting material for the manufacture of polyarylene ethers such as polyphenylene oxide, a valuable thermoplastic resin disclosed and claimed, for example, in A. S. Hay's U.S. Pat. No. 3,306,875.